This invention relates to electrostatographic reproduction apparatus and is particularly concerned with such apparatus for reproducing signal encoded images exhibited on a display surface in an automatic mode of operation.
In one well-known form of automatic electrostatographic reproduction apparatus, a moving photoconductive plate [photoreceptor] generally in the form of an endless surface, such as a drum, belt or the like, is first uniformly charged and the surface then exposed to a light pattern of the image sought to be reproduced thereby to discharge the charge in the areas where light strikes the plate. The undischarged areas of the plate thus form an electrostatic charge pattern in conformity with the configuration of the original image pattern. This electrostatic latent image may then be developed in visible form by applying a developer material to the plate using any one of a number of development means generally known and used in the art. Subsequent to the development operation, the now visible image is transferred from the plate to a sheet of final support material such as paper of the like and suitable affixed to it thereby forming a permanent print. One example of such a machine is described and illustrated in U.S. Pat. No. 3,640,615. This machine incorporates a stationary platen for an original document to be copied and an optical projection system for projecting an image of the document onto the photoconductive plate, which system has a moving mirror for scanning the document. As the mirror scans across the document the image is projected onto the photoreceptor, the movement of which is synchronized with that of the mirror. Instead of the miror being moved during scanning the document itself may be moved for example by mounting it on a reciprocating carriage.
It is known in the prior art to provide a display device, such as cathode ray oscilloscope, for the display of signal encoded data. The optical display can then be imaged onto a photoreceptor of an electrostatographic reproduction machine for example as described in U.S. Pat. No. 3,673,936. However, it is frequently desirable to encode an image in signals which are not efficiently utilized by the typical automatic electrostatic reproduction device of the kind described above in which the photoconductive plate is in motion during exposure. Such apparatus are typically geared for scanning an optical image media exhibited in its entirety at one time. The components of a signal encoded image are more efficiently displayed sequentially. In order to reproduce such images on an electrostatographic reproduction device of the kind described above it would be necessary to halt the device while the image is displayed on the display surface or in the alternative it would be necessary to provide extensive signal processing to produce the image as a scanning format on the display so that it can be utilized by the electrostatographic reproduction apparatus without halting it. However, the latter requires additional and frequently complex processing of the signals encoding the image and, particularly if the display device is a cathode ray oscilloscope, it is necessary to include apparatus for maintaining the image during scanning by the optical projection system of the apparatus.
The use of an image storage device, such as a photoconductive liquid crystal sandwich, in conjunction with an electrostatographic reproduction apparatus has been proposed for temporarily storing an image to be reproduced, this stored image then being imaged onto the photoconductive plate of the apparatus. One example of such use of an image storage device is to be found in U.S. Pat. No. 3,778,149.
As described above one way of exposing a photoconductive plate of an automatic electrostatographic reproduction apparatus to an image to be reproduced is to utilize a stationary optical system and means for moving the image carrier for scanning the image. However where such an image carrier is an intermediate image storage service which is to be exposed to information displayed sequentially on a display surface, it is necessary for the device to be held stationary during this exposure. During imaging onto the photoconductive plate it is important that the image carrier be moved synchronously with the photoconductive plate but the imaging step is completed before the completion of other steps in the electrostatographic process such as development, transfer and fixing. Accordingly it is desirable for the image carrier to be brought to a stationary position while the photoconductive plate is still moving. Various mechanisms for achieving this in electrostatographic reproduction machines having document scanning carriages have been proposed such as in U.S. Pat. No. 3,697,165 but these have tended to be rather complicated.